首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1526篇
  免费   108篇
  国内免费   24篇
耳鼻咽喉   21篇
儿科学   47篇
妇产科学   30篇
基础医学   239篇
口腔科学   26篇
临床医学   196篇
内科学   310篇
皮肤病学   42篇
神经病学   114篇
特种医学   133篇
外科学   180篇
综合类   87篇
一般理论   1篇
预防医学   90篇
眼科学   27篇
药学   65篇
中国医学   1篇
肿瘤学   49篇
  2021年   9篇
  2019年   11篇
  2018年   14篇
  2017年   11篇
  2016年   25篇
  2015年   18篇
  2014年   32篇
  2013年   77篇
  2012年   29篇
  2011年   61篇
  2010年   50篇
  2009年   48篇
  2008年   38篇
  2007年   68篇
  2006年   44篇
  2005年   38篇
  2004年   34篇
  2003年   37篇
  2002年   39篇
  2001年   35篇
  2000年   27篇
  1999年   35篇
  1998年   56篇
  1997年   55篇
  1996年   50篇
  1995年   35篇
  1994年   43篇
  1993年   44篇
  1992年   33篇
  1991年   22篇
  1990年   37篇
  1989年   55篇
  1988年   36篇
  1987年   44篇
  1986年   35篇
  1985年   17篇
  1984年   21篇
  1983年   17篇
  1982年   12篇
  1981年   12篇
  1980年   12篇
  1979年   14篇
  1978年   9篇
  1976年   14篇
  1975年   16篇
  1974年   9篇
  1971年   9篇
  1966年   9篇
  1963年   9篇
  1941年   11篇
排序方式: 共有1658条查询结果,搜索用时 15 毫秒
31.
Objective:Trichomonas vaginalis vaginal infections are often both asymptomatic and difficult to detect by current methods. We evaluated the ability of a newly developed polymerase chain reaction (PCR) assay to identify T. vaginalis in vaginal samples from pregnant and non-pregnant women.Methods: In the 1st study, we compared the prevalence of T. vaginalis detection by PCR and culture using Diamond's medium in 52 women with symptoms of vaginal infection. In the 2nd study, T. vaginalis was detected using PCR and wet mount microscopy in 131 asymptomatic pregnant women.Results: Among the women with symptoms of vaginitis, 7 (13.5%) were PCR-positive for T. vaginalis. Six of the PCR-positive women, but none of the PCR-negative women, were culture-positive for this organism. All but 1 of the women with candidal vaginitis or bacterial vaginosis were PCR-negative for T. vaginalis. Among the asymptomatic pregnant women, all of whom were negative for T. vaginalis by wet mount, l0 (7.6%) were PCR-positive for T. vaginalis.Conclusions: PCR offers a rapid and sensitive alternative to culture and microscopy for the detection of T. vaginalis vaginal infections in both symptomatic and asymptomatic women.  相似文献   
32.
Ischemic brain damage occurs in most patients with acute subdural hematoma, yet many aspects of the distribution and extent of this damage remain unexplained. Previous studies in rat model, which produces a region of infarction under the hematoma, have implicated an "excitotoxic" mechanism, suggesting that high concentrations of excitatory amino acids may exacerbate ischemic damage. A study is described in which local glucose utilization is measured 2 or 4 hours after induction of acute subdural hematoma in the rat. These changes are compared to those produced by introducing the same volume of inert silicone gel into the subdural space. Massive increases (up to 142%) in glucose utilization occurred throughout both hippocampi and in a variable zone around the ischemic core, but these had normalized by 4 hours after blood injection. Hippocampal hypermetabolism was not seen after introduction of the silicone mass, suggesting that diffusible substances from the clotted blood may be responsible for these changes. This transient hypermetabolism accords with an excitotoxic process, which may amplify brain damage after acute subdural hematoma.  相似文献   
33.
IL Ackerman  CA Karn  SC Denne  GJ Ensing  CA Leitch 《Pediatrics》1998,102(5):1172-1177
OBJECTIVE: The purpose of this study was to determine the effect of left-to-right shunting on the resting energy expenditure (REE), total energy expenditure (TEE), and energy intake in a group of 3- to 5-month-old infants with moderate to large unrepaired ventricular septal defects (VSDs) compared with age-matched, healthy infants. METHODS: Eight infants with VSDs and 10 healthy controls between 3 to 5 months of age participated in the study. Indirect calorimetry was used to measure REE and the doubly-labeled water method was used to measure TEE and energy intake. An echocardiogram and anthropometric measurements were performed on all study participants. Daily urine samples were collected at home for 7 days. Samples were analyzed by isotope ratio mass spectrometry. Data were compared using analysis of variance. RESULTS: No significant differences were found in REE (VSD, 42.2 +/- 8.7 kcal/kg/d; control, 43.9 +/- 14.1 kcal/kg/d) or energy intake (VSD, 90.8 +/- 19.9 kcal/kg/d; control, 87.1 +/- 11.7 kcal/kg/d) between the groups. The percent total body water was significantly higher in the VSD infants and the percent fat mass was significantly lower. TEE was 40% higher in the VSD group (VSD, 87.6 +/- 10.8 kcal/kg/d; control, 61.9 +/- 10.3 kcal/kg/d). The difference between TEE and REE, reflecting the energy of activity, was 2.5 times greater in the VSD group. CONCLUSIONS: REE and energy intake are virtually identical between the two groups. Despite this, infants with VSDs have substantially higher TEE than age-matched healthy infants. The large difference between TEE and REE in VSD infants suggests a substantially elevated energy cost of physical activity in these infants. These results demonstrate that, although infants with VSDs may match the energy intake of healthy infants, they are unable to meet their increased energy demands, resulting in growth retardation.  相似文献   
34.
The Dunning H rat prostate tumor (R3327H) is a widely used experimental model of human prostatic adenocarcinoma (CaP). The Dunning H tumor has been characterized as androgen-sensitive, androgen-receptor (AR) positive, prostate-specific antigen and prostatic acid phosphatase (PAP) positive. To date, the tumor has been maintained by serial passage in vivo because of the lack of an in vitro cell line that retains the characteristics of the in vivo tumor. The objective of the present study was to establish a propagable cell line from R3327H adenocarcinoma that maintained androgen sensitivity and expression of AR, PSA and PAP. Tissue harvested from an in vivo R3327H tumor was dissociated with collagenase and placed into Richter's improved media (with supplements). A cytokeratin-positive epithelial cell line (HUNC- E) and a vimentin-positive stromal cell line (HUNC-S) were generated from the primary culture, subcultured continuously for >300 days, and passaged >50 times. Survival of the HUNC-E cell line in vitro depended on several media supplements, including nicotinamide, insulin, transferrin, selenium and epidermal growth factor (EGF). HUNC-E cells expressed AR and produced PSA and PAP throughout the culture period, as confirmed by immunocytochemistry and Western blot analyses. Addition of 14 nM testosterone (T) or dihydrotestosterone (DHT) to HUNC-E cells, stimulated DNA synthesis as well as anchorage-independent growth and PSA production, which demonstrated the androgen-sensitive nature of the cells in vitro. When HUNC-E and HUNC-S cells were combined in a 3:1 ratio and introduced subcutaneously into syngeneic male hosts, tumors formed in 2/3 animals with an average latency of 7 months. RT-PCR and immunocytochemical characterization of the HUNC cell lines revealed that the cells expressed several growth factors and their cognate receptors, including HGF, TGF-alpha and the TGF-betas, indicating the establishment of potential autocrine loops in the neoplastic cells. The HUNC-E and HUNC-S CaP cell lines, which retain the characteristics of the epithelial and stromal components of the in vivo R3327H tumor, will allow a more thorough and informative molecular and biological analysis of prostatic adenocarcinoma.   相似文献   
35.
A study was carried out to find out the effects of prior physical activity, sports participation and prior military training on the incidence of stress fractures among Gentlemen Cadets (GC''s) undergoing military training at Indian Military Academy (IMA). One thousand and fourteen GC''s were followed up for a period of 12 weeks. Thirty-seven GC''s developed stress fractures during the study period. The incidence of stress fractures was significantly higher in GC''s without any prior military training (p=0.0009). They were compared with 100 healthy controls drawn from the study population to study the influence of the other mentioned factors. There was no significant association between prior physical activity and stress fractures (OR=0.74, 95% CL=0.26 to 2.05, p=0.688). There was also no significant relationship between sports participation and stress fractures (OR=0.79. 95% CCL=0.35 to 1.81, p=0.684).KEY WORDS: Risk factors, Stress fractures  相似文献   
36.
With the increasing incidence of multifetal gestations, it is essential for the clinician to appreciate the benefit of ultrasound evaluation in these pregnancies. Multifetal gestation pregnancies are at increased risk for a range of both antepartum and intrapartum complications, such as intrauterine growth restriction, premature delivery, congenital anomalies, cord accidents, malpresentations, placenta previa, and abruptio placentae. First-trimester ultrasonic evaluation, amniotic fluid assessment, monitoring of fetal growth, diagnosing the twin-to-twin transfusion syndrome, and assessment of fetal anomalies will be reviewed. An early and accurate assessment of amnionicity and chorionicity are paramount in these gestations. The impact of chorionicity, in particular, can have profound consequences in the management of multifetal gestations. The determination of chorionicity onultrasonic evaluation in a multifetal gestations. The determination of chorionicity on ultrasonic evaluation in a multifetal pregnancy should be determined in a systematic way between 10-14 weeks' gestation. The amniotic fluid volume should be routinely assessed when performing an ultrasonic evaluation in a multifetal pregnancy. Amniotic fluid changes may serve as the only useful indicator to a potential pathological condition. In addition, evaluation of fetal growth in twins is essential, because these pregnancies are at increased risk for growth restriction and increased perinatal mortality rates compared to singletons. Finally, a careful anatomical evaluation in mulitifetal gestation is important because twin pregnancies have higher rates of anomalies than their singleton counterparts.  相似文献   
37.
38.
Cytogenetic and histologic correlations in malignant lymphoma   总被引:9,自引:0,他引:9  
Although a number of studies have indicated correlations between histologic subtypes of tumors and certain nonrandom chromosome changes, cytogenetic studies of lymphoma are in an early stage compared to those of leukemia. No comprehensive analysis of available data has so far been attempted in the literature either. Here we present an analysis of chromosome changes and their correlation with subtypes of lymphoma studied by conventional histology and cell surface markers, as observed in two sets of data: a group of 65 karyotypically abnormal tumors sequentially ascertained and studied by us during the period January 1, 1984 to April 30, 1985, and a larger data set derived by combining our data with those from two published series from the University of Minnesota that are comparable to our data. These combined data, which comprise the largest data set on the cytogenetics of lymphomas assembled so far, enabled a comprehensive analysis of correlation between chromosome change and tumor histology and the patterns of chromosome instability in these tumors. We found several significant associations, some previously described and others now recognized, between nonrandom chromosome gains, breaks, translocations, and deletions and histologic subtypes of tumors that characterize lymphomas. The data indicate that finding of chromosome breaks at certain sites (eg, 8q24, 14q32, 18q21) is of diagnostic value in dealing with cases of unusual lymphoma. Furthermore, nonrandom chromosome breakage exhibited three distinct patterns that reflected three levels of etiologically relevant genetic change.  相似文献   
39.
Respiratory viruses in children admitted to hospital in Edinburgh 1972-1985   总被引:1,自引:0,他引:1  
The temporal incidence of respiratory viruses identified in children admitted to an Edinburgh hospital over a period of 14 years, 1972-1985, is described, Respiratory syncytial (RS) virus was identified most often, usually (but not in 1979 and 1985) with single peaks of activity in the winter months. Influenza virus infections were seen in the winter and spring but we failed to find evidence of interference between RS and influenza virus. Of the viruses studied, the parainfluenza viruses were the least predictable in their epidemiological behaviour. The results of this study are compared with those of others and the role of certain aspects of the weather is considered.  相似文献   
40.
Hafenrichter  DG; Wu  X; Rettinger  SD; Kennedy  SC; Flye  MW; Ponder  KP 《Blood》1994,84(10):3394-3404
Hepatic gene therapy could be used to treat a number of inherited blood diseases such as hemophilia or thrombophilia. Although liver-directed retroviral transduction can result in long-term gene expression in vivo, the low level of protein production has limited its clinical application. We reasoned that the insertion of liver-specific promoters into retroviral vectors would increase gene expression in vivo. The 347- bp human alpha 1-antitrypsin (hAAT), the 810-bp murine albumin (mAIb), the 490-bp rat phosphoenolpyruvate carboxykinase (rPECK), and the 596- bp rat liver fatty acid binding protein promoters were inserted into a Moloney murine leukemia retroviral backbone containing the hAAT reporter gene. Vectors that produced appropriately sized RNA and hAAT protein in vitro were tested in vivo by transducing regenerating rat livers. Long-term serum expression of the hAAT reporter gene was normalized to retroviral transduction efficiency as determined by using a polymerase chain reaction-based assay of genomic DNA from transduced rat livers. The hAAT, mAIb, and rPEPCK promoters were, respectively, 35- , 8-, and 0.02-fold as strong as the previously studied constitutive Pol-II promoter. We conclude that the hAAT promoter resulted in the highest expression from a retroviral vector and may result in therapeutically significant expression of other clinically significant blood proteins.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号